$40$ is what percent of $50$ ?
Solution: Having a percent of something means that you get that percent out of every $100$ We can set up a proportion to find out what percent of $50$ we need to take to get $40$ $ \dfrac{{\text{percent}}}{100} = \dfrac{{\text{part}}}{{\text{whole}}}$ Which things do we know, and what are we trying to find? We are trying to find the ${\text{percent}}$ . Is $50$ the ${\text{part}}$ or the ${\text{whole}}$ The $50$ is the ${\text{whole}}$ . This means the ${\text{part}}$ is $40$ $ \dfrac{{\text{percent}}}{100} = \dfrac{{40}}{{50}}$ If we multiply the denominator of the fraction on the right by $2$ , it will be the same denominator of the fraction on the left. To keep things equal, let's also multiply the numerator on the right by $2$ $ \dfrac{{\text{percent}}}{100 } = \dfrac{{40 \times 2}}{{50 \times 2}}$ $ \dfrac{{\text{percent}}}{100 } = \dfrac{{80}}{{100}}$ $ {\text{percent}} = {80}$ So $40$ is $80\%$ of $50$.